2,582 research outputs found
Weak lensing observations of the "dark" cluster MG2016+112
We investigate the possible existence of a high-redshift (z=1) cluster of
galaxies associated with the QSO lens system MG2016+112. From an ultra-deep R-
and less deep V- and I-band Keck images and a K-band mosaic from UKIRT, we
detect ten galaxies with colors consistent with the lensing galaxy within
225h^{-1} kpc of the z=1.01 lensing galaxy. This represents an overdensity of
more than ten times the number density of galaxies with similar colors in the
rest of the image. We also find a group of seven much fainter objects closely
packed in a group only 27h^{-1} kpc north-west of the lensing galaxy. We
perform a weak lensing analysis on faint galaxies in the R-band image and
detect a mass peak of a size similar to the mass inferred from X-ray
observations of the field, but located 64" northwest of the lensing galaxy.
From the weak lensing data we rule out a similar sized mass peak centered on
the lensing galaxy at the 2 sigma level.Comment: 9 pages, 10 figures, submitted to A&A version with figure 4 at higher
resolution can be downloaded from
http://www.mpa-garching.mpg.de/~clowe/mg2016aa.ps.g
Eigenvector localization as a tool to study small communities in online social networks
We present and discuss a mathematical procedure for identification of small
"communities" or segments within large bipartite networks. The procedure is
based on spectral analysis of the matrix encoding network structure. The
principal tool here is localization of eigenvectors of the matrix, by means of
which the relevant network segments become visible. We exemplified our approach
by analyzing the data related to product reviewing on Amazon.com. We found
several segments, a kind of hybrid communities of densely interlinked reviewers
and products, which we were able to meaningfully interpret in terms of the type
and thematic categorization of reviewed items. The method provides a
complementary approach to other ways of community detection, typically aiming
at identification of large network modules
The challenge of detecting intracluster filaments with Faraday Rotation
The detection of filaments in the cosmic web will be crucial to distinguish
between the possible magnetogenesis scenarios and future large polarization
surveys will be able to shed light on their magnetization level. In this work,
we use numerical simulations of galaxy clusters to investigate their possible
detection. We compute the Faraday Rotation signal in intracluster filaments and
compare it to its surrounding environment. We find that the expected big
improvement in sensitivity with the SKA-MID will in principle allow the
detection of a large fraction of filaments surrounding galaxy clusters.
However, the contamination of the intrinsic Faraday Rotation of background
polarized sources will represent a big limiter to the number of objects that
can be significantly detected. We discuss possible strategies to minimize this
effect and increase the chances of detection of the cosmic web with the large
statistics expected from future surveys.Comment: 16 pages, accepted to Galaxie
The Kinematic Properties of the Extended Disks of Spiral Galaxies: A Sample of Edge-On Galaxies
We present a kinematic study of the outer regions (R_25<R<2 R_25) of 17
edge-on disk galaxies. Using deep long-slit spectroscopy (flux sensitivity a
few 10^-19 erg s^-1 cm^-2 arcsec^-2), we search for H-alpha emission, which
must be emitted at these flux levels by any accumulation of hydrogen due to the
presence of the extragalactic UV background and any other, local source of UV
flux. We present results from the individual galaxy spectra and a stacked
composite. We detect H-alpha in many cases well beyond R_25 and sometimes as
far as 2 R_25. The combination of sensitivity, spatial resolution, and
kinematic resolution of this technique thus provides a powerful complement to
21-cm observations. Kinematics in the outer disk are generally disk-like (flat
rotation curves, small velocity dispersions) at all radii, and there is no
evidence for a change in the velocity dispersion with radius. We place strong
limits, few percent, on the existence of counter-rotating gas out to 1.5 R_25.
These results suggest that thin disks extend well beyond R_25; however, we also
find a few puzzling anomalies. In ESO 323-G033 we find two emission regions
that have velocities close to the systemic velocity rather than the expected
rotation velocity. These low relative velocities are unlikely to be simply due
to projection effects and so suggest that these regions are not on disk-plane,
circular orbits. In MCG-01-31-002 we find emission from gas with a large
velocity dispersion that is co-rotating with the inner disk.Comment: 18 pages, 14 figures, accepted for publication in Ap
Pattern discovery in adverse event data
Imperial Users onl
Small Bodies Science with Twinkle
Twinkle is an upcoming 0.45m space-based telescope equipped with a visible
and two near-infrared spectrometers covering the spectral range 0.4 to
4.5{\mu}m with a resolving power R~250 ({\lambda}<2.42{\mu}m) and R~60
({\lambda}>2.42{\mu}m). We explore Twinkle's capabilities for small bodies
science and find that, given Twinkle's sensitivity, pointing stability, and
spectral range, the mission can observe a large number of small bodies. The
sensitivity of Twinkle is calculated and compared to the flux from an object of
a given visible magnitude. The number, and brightness, of asteroids and comets
that enter Twinkle's field of regard is studied over three time periods of up
to a decade. We find that, over a decade, several thousand asteroids enter
Twinkle's field of regard with a brightness and non-sidereal rate that will
allow Twinkle to characterise them at the instrumentation's native resolution
with SNR > 100. Hundreds of comets can also be observed. Therefore, Twinkle
offers researchers the opportunity to contribute significantly to the field of
Solar System small bodies research.Comment: Published in JATI
Warm Debris Disks Candidates in Transiting Planets Systems
We have bandmerged candidate transiting planetary systems (from the Kepler
satellite) and confirmed transiting planetary systems (from the literature)
with the recent Wide-field Infrared Survey Explorer (WISE) preliminary release
catalog. We have found 13 stars showing infrared excesses at either 12 and/or
22 microns. Without longer wavelength observations it is not possible to
conclusively determine the nature of the excesses, although we argue that they
are likely due to debris disks around the stars. If confirmed, our sample ~
doubles the number of currently known warm excess disks around old main
sequence stars. The ratios between the measured fluxes and the stellar
photospheres are generally larger than expected for Gyr-old stars, such as
these planetary hosts. Assuming temperature limits for the dust and emission
from large dust particles, we derive estimates for the disk radii. These values
are comparable to the planet's semi-major axis, suggesting that the planets may
be stirring the planetesimals in the system.Comment: Submitted to A&A: 21 October 2011 / Accepted for publication in A&A:
27 February 201
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